1. Field of the Invention
The present invention relates to a circuit board that has land patterns for soldering terminals of electronic components, and in particular, to a circuit board that is adapted to prevent an adverse effect caused on an electronic component due to flux and the like that are produced at the time of soldering.
2. Description of the Related Art
In general, when various electronic components are mounted on a circuit board, a wiring pattern is formed on the circuit board and terminals of the electronic components are soldered to land patterns of this wiring pattern. In such a soldering process, for the purpose of securing wettability between the land patterns of the circuit board and the terminals of the electronic components and realizing satisfactory soldering, for example, soldering processing is performed by applying flux to the circuit board or using solder containing flux. However, since the flux consists of water and active components and has a water absorption property and a moisture absorption property, when the flux intrudes into the electronic components, the flux changes to a film having a hydrophilic nature. This film acts as a medium for an electrochemical reaction to result in causing a failure such as deterioration in insulation due to electrolytic etching. As a conventional measure for preventing such a failure due to the flux, Japanese Utility Model Laid-Open Publication No. 07-003158 proposes a circuit board that is constituted to control intrusion of a foreign material such as flux into electronic components mounted on a circuit board by forming a hole in the bottom surface of an electronic component such as a surface wave filter on the circuit board and permitting the foreign material such as the flux, which is produced at the time of soldering, to escape from the hole.
In recent years, various electronic devices tend to be reduced in size and thickness. In addition, a circuit board further reduced in size is demanded as a circuit board to be built in the electronic devices. Thus, in recent years, electronic components to be mounted on the circuit board tend to be mounted more densely. Consequently, in the case in which a distance between two electronic components is short, and for example, a wiring member such as a flat cable is soldered to be connected to the electronic components after the circuit board is manufactured, when other electronic components are mounted near a land pattern of the flat cable, it is likely that flux, which is produced at the time of the soldering of the flat cable, directly intrudes into the electronic components near the land pattern. In such a case, even if a hole is formed in the bottom surface of an electronic component as described in the Japanese Utility Model Laid-Open Publication No. 07-003158, it is difficult to effectively prevent the flux that is produced at the time of soldering of the flat cable to be attached to the circuit board after the circuit board is manufactured.